Heavy hammer

: I am looking for the meaning of the phrase "gone under a heavy hammer" as in under the heavy hammer of a military-type government or something similar. "Under the hammer" I know means sold at an auction but this meaning does not fit how this is being used in the context I am reading.

in metal-working, farriers, smiths, tinkers etc use different weights of hammer depending on the job. shaping/flattening a larger piece of metal would be started with a heavier hammer than used for the detailed work.
there is also a machine used in industry called a 'trip hammer' and there are other similar devices more powerful than a hand-hammer, but which are still called 'hammers' even though the resemblance is almost non-existent.

any device which delivers physical force to flatten without puncturing or cutting could probably be termed an 'hammer' so a thorough search for the origin might be wide-ranging.